1. Field of the Invention
This invention relates to a low-noise level automotive internal combustion engine, and more particularly to the engine equipped with a bearing beam structure for supporting a crankshaft.
2. Description of the Prior Art
As a cause of engine noise, there is vibration noise emitted from a cylinder block skirt or lower section and an oil pan which noise is caused by the vibration of a cylinder block. In order to reduce such vibration noise it seems enough to suppress vibration, due to explosion torque, applied to a crankshaft by increasing the rigidity of the cylinder block. However, this unavoidably leads to the increase in cylinder block wall thickness and accordingly to a great increase in engine weight, thereby giving rise to new problems such as reduced fuel economy. In view of this, a variety of propositions have been made to improve the rigidity of the cylinder block while suppressing the increase in cylinder block weight. Of these propositions, particular attention has been paid to the employment of a bearing beam structure which securely connects a plurality of bearing caps for directly support the crankshaft to improve the strength of bearing caps and engine parts associated with them.